The present invention relates to a method and apparatus for searching a contour line of a cutout image in order to cut out and extract a necessary image region.
For example, in the case of printing a merchandise catalog, since a background is photographed in the merchandise photograph used as an original image of printing, it is necessary to erase the background of the merchandise so as to display only the merchandise.
For this reason, the following method is adopted: A mask film is provided, on which only an image portion is made transparent and other portions are made opaque. The mask film is put on an original image so as to erase the unnecessary background, and the photographic copying operation is conducted. In this way, an image in which only the merchandise is displayed can be provided.
Conventionally, the following mask forming techniques are known.
(1) Using an engraving scanner, Y (yellow), M (magenta), C (cyan) and K (black) images are read out from the original color image. In this case, image data of K (black) is used, and the mask film is made.
(2) A peel-off film is put on each print of Y, M, C and K. Then a skilled workman makes a mask film with a cutter in such a manner that the print is cut along a desired contour of the image.
(3) On an image processing working station for processing digitized image data, an operator traces a displayed image using a pointing device.
According to the above techniques of the prior art, the following problems may be encountered.
According to the technique described in item (1), a desired image is masked and extracted from the entire image only by the difference of density. Therefore, it is impossible to extract the desired image correctly.
According to the techniques described in item (2), it takes time to make a mask film, and further a heavy burden is imposed on the eyes of a work man, so that the working environment is deteriorated. Further, skilled workers are shorthanded, and the quality of obtained mask films fluctuates because it depends on the technique of workers.
According to the technique described in item (3), in the same manner as that of item (2), so that the same problems may be encountered, and there is a demand of automatizing the operation.
As described above, it is difficult to enhance the accuracy of extraction of a cutout image only by the skilled labor.
In order to solve the above problems, Japanese Patent Publication No. 5745/1988 (63-5745) discloses an apparatus in which a desired image can be cut out in the following manner: Using a difference between the density of an image region to be cut out and the density of a background, and also using a difference between the colors, a contour line of the image to be cut out is automatically found, and according to the found contour line, the desired image is cut out.
However, when the contour line is found in accordance with the difference of density and color according to the above method, there are various types of original images to be cut out. In some cases, a difference between the image region to be cut out and the background is very small, and it is difficult to accurately cut out a desired image.
Conventionally, a contour line of the image to be cut out is found from image data in accordance with a predetermined contour extracting condition (cutout condition). Therefore, the conventional method does not accurately correspond to a change in the background of the original image. Although cutout operations can be accurately conducted in a specific original image, it is difficult to stably cut out various original images.